1. Field of the Invention
The present invention generally relates to a cylinder block structure for an engine and more particularly to a cylinder block structure which can reduce noises radiation from the engine.
2. Description of the Related Art
One of conventional cylinder blocks for an engine is disclosed in, for example, Japanese Utility Model Registration No. 2,514,559 entitled "CYLINDER BLOCK STRUCTURE" issued to Suzuki Kabushiki Kaisha of Shizuoka, Japan. Referring to FIG. 6 of the accompanying drawings, illustrated is the first drawing of this prior art reference. In this conventional cylinder block structure, a single cooling water jacket c and a plurality of oil dropping passages or chutes d are formed in a cylinder block a of an engine. The water jacket c extends surrounding a plurality of cylinder bores e and defines cylinder bore walls b around the cylinder bores e respectively. Intermediate marginal areas g are defined between adjacent cylinder bores e. The oil chutes d connect a cylinder head (not shown) to a crankcase f such that an oil descends into the crankcase f from the cylinder head and a blow-by gas ascends into the cylinder head from the crankcase f. In the conventional arrangement, the oil chutes d are formed in the areas g between adjacent cylinder bores e in order to effectively use these areas g.
In recent years, cylinder blocks are often fabricated of aluminum, instead of cast iron, to reduce the weight of the engine. However, the aluminum is weaker than the cast iron so that if the cylinder block a shown in FIG. 6 is made of aluminum, noises generated upon combustion in the cylinder bores e penetrate a cylinder block wall h and leak to the outside. These noises are significant in diesel engines (particularly diesel engines equipped with a supercharger) of which combustion pressure in the cylinder bores e is high.
In addition to the oil chutes d, cylinder head bolt holes i are also formed in the intermediate marginal areas g of the cylinder block a for bolts connecting the cylinder head with the cylinder block a. In actuality, therefore, the intermediate areas g cannot be used solely for the oil chutes d, and a thicker wall is required to accommodate the oil chutes d. Accordingly, the cylinder block a swells out partly and occupies a relatively large space in an engine room. Moreover, bulk heads (not shown) exist between adjacent cylinder bores e so that the cylinder block a should be designed to avoid the bulk heads. This also makes the cylinder block a expand outward and occupy a large space in the engine room.